Various heat transfer recording methods have been known so far. Among these methods, dye diffusion transfer recording systems attract attention as a process that can produce a color hard copy having an image quality closest to that of silver salt photography (see, for example, “Joho Kiroku (Hard Copy) to Sono Zairyo no Shintenkai (Information Recording (Hard Copy) and New Development of Recording Materials)” published by Toray Research Center Inc., 1993, pp. 241-285; and “Printer Zairyo no Kaihatsu (Development of Printer Materials)” published by CMC Publishing Co., Ltd., 1995, p. 180). Moreover, this system has advantages over silver salt photography: it is a dry system, it enables direct visualization from digital data, it makes reproduction simple, and the like.
In this dye diffusion transfer recording system, a heat-sensitive (thermal) transfer sheet (hereinafter also referred to as an ink sheet) containing dyes is superposed on a heat-sensitive (thermal) transfer image-receiving sheet (hereinafter also referred to as an image-receiving sheet), and then the ink sheet is heated by a thermal head whose exothermic action is controlled by electric signals, in order to transfer the dyes contained in the ink sheet to the image-receiving sheet, thereby recording an image information. Three colors: cyan, magenta, and yellow, are used for recording a color image by overlapping one color to other, thereby enabling transferring and recording a color image having continuous gradation for color densities.
On the other hand, an example of fields in which new applications of this dye diffusive transfer recording system are being developed, is that of heat transfer recording labels, or heat transfer recording tags, for use in POS (Point Of Sales) systems. It is relatively unusual for this system to be used in severe conditions for a long period of time, in current food label applications and cloth tag applications. However, opportunities to use this system have increased in distribution management applications such as delivery labels and air baggage tags, and it is demanded of this system to enable precise recording of, for example, bar codes, and to provide a high-quality image. Also, it is desired to improve the paper strength of heat transfer recording image-receiving paper, because there is the case in which a recording material is exposed to severe conditions.
JP-A-9-220863 (“JP-A” means unexamined published Japanese patent publication) discloses that crepe paper or extensible paper is used as a support of the image-receiving sheet. However, when this crepe paper or extensible paper is used as the support, there is the problem that moisture is absorbed in the paper during the course of the process from coating step to drying step, and also the moisture remains in the paper even after the paper is dried, causing a reduction in the sharpness of a receptor layer over time.
In the image formation that is performed using the above-described thermal transfer sheet with a thermal head, when the processing for the image formation is conducted at a high speed, and if a substrate film is a thermoplastic film such as a polyester film, problems arise that the thermal head welds the base film of an ink sheet because the thermal head has been heated at a high temperature, so that an excellent traveling of the thermal head is deteriorated, and thereby a failure such as breakage and wrinkle occurs in the thermal transfer sheet. Besides, when the processing is conducted at a high speed in the image formation, the heating time of the thermal head becomes insufficient, and the dyes transferred to the receptor layer stay in the vicinity of the surface of the receptor layer without diffusing sufficiently into the whole receptor layer. Therefore, there arises a problem that deterioration in fastness to light of images is caused.